This invention relates to the fabrication of integrated circuits (ICs) and, more particularly, to the removal of hardened organic materials during the fabrication of ICs.
In a number of IC fabrication sequences of practical importance, it is necessary to remove from the IC structure being fabricated a highly adherent hardened pattern made of an organic material. Ideally, the removal of the material should be accomplished quickly and in a manner that does not deleteriously affect any of the other materials included in the IC structure.
A known fabrication method available for making high-resolution metallization patterns in IC structures is the so-caled lift-off process. In one version of this process, a patterned layer made of a heat-hardened organic material is formed on an underlying layer. Preselected portions of the underlying layer are not covered by the patterned layer. A metallic layer is then deposited on top of the patterned layer and on top of the uncovered portions of the underlying layer. Thereafter, the hardened pattern is removed whereby the metallic regions deposited thereon are "lifted off". The metallic regions remaining on the underlying layer constitute the desired metallization pattern required for the IC structure.
Other IC fabrication processes are known in which a pattern of organic material must be removed from the structure being made. For example, it is known to employ an organic pattern as a mask for reactive ion etching. During the etching step, the masking pattern may be hardened by the impingement of ions thereon. Rapid and selective removal of the hardened pattern, without substantially affecting other materials in the IC structure, then becomes a difficult task.
Heretofore, various dry etching techniques and liquid solvents have been utilized in IC fabrication sequences to remove hardened organic materials. But, in some cases of practical importance, this removal occurs in an undesirably slow manner and/or by a process that deleteriously etches or otherwise attacks other materials in the IC structure.
Accordingly, continuing efforts have been made by workers in the IC art directed at trying to develop IC fabrication processes in which hardened organic materials utilized as masking patterns can be rapidly and reliably removed from the structure being made. It was recognized that such efforts, if successful, could significantly improve the quality and lower the cost of IC devices.